The aim of this project is to obtain structural information on polynucleotides and to provide insights into the factors which control structure, principally through X-ray fiber diffraction and model building studies. Current areas include;1) determination of the helical parameters of DNA in concentrated solutions by diffraction techniques; 2) characterizing the secondary structures induced in DNA by a variety of solvents and conditions, using new sample-handling techniques which give ordered diffraction patterns even in the presence of large amounts of solvent.